Fix #374: describe automount of /run, /tmp and tmpfiles.d support

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/bootstrap.md

@@ -19,11 +19,14 @@ Bootstrap
 12. Remount `/` read-write if `/` is listed in `/etc/fstab` without `ro`
 13. Call 1st level hooks, `HOOK_ROOTFS_UP`
 14. Mount all file systems listed in `/etc/fstab` and swap, if available.
-    On mount error `HOOK_MOUNT_ERROR` is called.  After mount, regardless
-    of error, `HOOK_MOUNT_POST` is called
+    Finit verifies that `/dev/shm`, `/dev/pts`, `/run`, and `/tmp` are
+    mounted.  If not, Finit mounts them as `tmpfs` because otherwise the rest
+    of the boot may fail.  On any mount error `HOOK_MOUNT_ERROR` is called.
+    After mount, regardless of error, `HOOK_MOUNT_POST` is called
 15. Enable SysV init signals
 16. Call 2nd level hooks, `HOOK_BASEFS_UP`
-17. Cleanup stale files from `/tmp/*` et al, handled by `bootmisc` plugin
+17. Cleanup stale files from `/tmp/*` et al and (re)create temporary files and
+    directories according to [tmpfiles.d(5)][], handled by `bootmisc` plugin
 18. Load kernel params from `/etc/sysctl.d/*.conf`, `/etc/sysctl.conf`
     et al. (Supports all locations that SysV init does.), handled by
     `procps` plugin
@@ -56,4 +59,5 @@ well before all 'S' runlevel tasks are started.  This could be used with
 system images that are created read-only and all configuration is stored
 on external media.
 
-[run-parts(8)]: http://manpages.debian.org/cgi-bin/man.cgi?query=run-parts
+[run-parts(8)]:  http://manpages.debian.org/cgi-bin/man.cgi?query=run-parts
+[tmpfiles.d(5)]:  https://www.freedesktop.org/software/systemd/man/tmpfiles.d.html

doc/plugins.md

@@ -28,9 +28,16 @@ For your convenience a set of *optional* plugins are available:
   system and runs at `HOOK_BASEFS_UP`.  The `/var`, `/run`, and `/dev`
   file systems must be writable for this plugin to work.
 
-  Note: On an embedded system both `/var` and `/run` can be `tmpfs` RAM
-  disks and `/dev` is usually a `devtmpfs`.  This must be defined in the
-  `/etc/fstab` file and in the Linux kernel config.
+  This plugin is a wrapper for the [tmpfiles.d(5)][] implementation that
+  Finit has.  Capable but limited: no aging, attributes, or subvolumes.
+
+  By default, `/lib/finit/tmpfiles.d` carries all the default .conf
+  files distributed with Finit.  It is read first but can be overridden
+  by any of the standard tmpfiles.d directories, e.g. `/etc/tmpfiles.d`.
+
+  > **Note:** On an embedded system both `/var` and `/run` can be `tmpfs`
+  > RAM disks and `/dev` is usually a `devtmpfs`.  This must be defined
+  > in the `/etc/fstab` file and in the Linux kernel config.
 
 * *dbus.so*: Setup and start system message bus, D-Bus, at boot.
   _Optional plugin._
@@ -50,8 +57,11 @@ For your convenience a set of *optional* plugins are available:
   customized at build-time using the `--with-hook-scripts-path=PATH`
   argument to `configure`.
 
-* *hotplug.so*: Setup and start either udev or mdev hotplug daemon, if
-  available.  Enabled by default.
+* *hotplug.so*: Replaced with `/lib/finit/system/10-hotplug.conf`, which
+  checks for `udevd` and `mdev` at boot.  This file can be overridden by a
+  file in `/etc/finit.d/10-hotplug.conf`.
+
+  Enabled by default.
   
   > See the [Services](config.md#services) section in the configuration
   > guide for an example how to run `mdevd`, alternative to plain mdev.
@@ -217,3 +227,5 @@ Plugins like `tty.so` extend finit by acting on events, they are called
 I/O plugins and are called from the finit main loop when `poll()`
 detects an event.  See the source code for `plugins/*.c` for more help
 and ideas.
+
+[tmpfiles.d(5)]: https://www.freedesktop.org/software/systemd/man/tmpfiles.d.html